Method of making enriched radioisotopes by cation fixation



United States Patent O fifice 3,167,479 Patented Jan. 26, 1965 The present invention relates to a method of making enriched radiosotopes and more particularly is directed to a novel method of producing high specific activity isotopes in considerably less time than any known process of the prior art. Such method includes the steps of cation fixation as an important element thereof.

Until the advent of the present invention the most convenient means of obtaining a number of artificial radioactive elements has consisted of either the separation of the desired element from fission products or the activation of a stable nuclei of a suitable element by neutrons from nuclear reactors. The former process of necessity is limited to those isotopes occurring in sufificient yields in the fission product spectrum. The latter process has the disadvantage that the product nuclei are often isotopic with the parent material; as a result the specific activities of such isotopes are necessarily limited and oftentimes can only be enhanced by prolonged irradiation in a high flux nuclear reactor.

My invention is in part based upon what may be termed cation fixation and makes use in the preferred embodiment hereof, of the imperfect lattices of substituted aluminum silicates. Generally speaking, the present process involves the introduction of the ionic species desired into such a lattice structure, the subsequent kation of such ions, removal of the not-fixed ions, neutron irradiation of the composite structure and finally the preferential'extraction of those nuclei which have gained recoil energy through the neutron, gamma (hereinafter referred to as the my) process, and thereby become removed from the fixed sites of the aluminum silicate lattice structures.

' I The specific details of my invention to enable one skilled in the art to practice the same are set out below.

One of the-,more important aspects of my invention is directed to the production of cobalt. In the conven tional' process of forming such material, cobalt is placed in a nuclear reactor where the atoms gain an extra neutron. As is well known to those skilled in this field the cobalt must remain in the reactor for several years in order that cobalt of high specific activity is obtained. In distinction to such prior art processes by the practice of the presentinvention, one is able to make such cobalt in only several months rather than several years. I

" have thus been able to make and segregate useful quanti ties of cobalt approximately twenty times faster than is possible with the conventionalprocesses. Similar enhanced reaction and separation times are likewise made available for a number of other cation species including for example, barium, sodium, magnesium, aluminum, potassium, calcium and scandium.

Furthermore, by the practice of my invention it is possible to more quickly, conveniently and expeditiously produce nuclear reaction products which differ in atomic number from the atomic number of the orginal nuclei which is placed upon the cation fixation member. Generally speaking, by such process I can carry out not only (nuetron, gamma) reactions but other reactions such as (neutron, proton) and (neutron, alphaparticle) likewise. These aspects too of my invention will be considered in the detail required for the practice of my process. 7

. Accordingly, a primary object of my invention is to provide a novel method of making cation radioisotopes which is considerably faster and more convenient than any known process of accomplishing a similar result.

Another important object of my invention is to provide a nuclear reaction process which includes as an important step thereof the fixing of nuclei of material to undergo such reaction on inorganic ion exchange materials, particularly clays, which are resistant to neutron flux.

A more specific object of my invention is to provide a.

new method of making radioactive cobalt, i.e., cobalt.

Another more specific object of my invention is to provide a new method of making radioactive barium, i.e., barium Other objects of my invention include the method of making antimony from tin cobalt from nickel and scandium from vanadium by various nuclear reactions, all of such reactions involving cation fixation.

These and other objects, features and advantages of my invention will become apparent to those skilled in this particular art from the following detailed disclosure thereof.

Before considering some of the specific examples of the present process, some brief introduction should first be had to the theoretical principles which underlie it. As is known, clay minerals, which are a family of naturally occurring aluminum silicates, contain both within and without their Al-OSi lattice structure sites for additional cations. This is What is referred to at times as imperfect lattice structures and such has been made use of for years in employing these materials for their ion exchange capabilities. Under certain circumstances the cations which are applied to the ion exchangematerial readily exchange and are substituted withother cations; under other circumstances, I have found that such cations can be made non-exchangeable or at best, exchangeable with some considerable difliculty. It is under the latter circumstances that I have been able to fix the cation in the aluminum silicate'clay which is of particular importance in the practice of my invention.'

In the present specification and for reasons of ready availability in carrying outthe experimental processes which led to my invention the cation fixation means used was aluminum silicate clays. It will be appreciated that other similar materials may be employedfor this purpose without departing from the spirit or scope of my invention. Such clays were selected both because the cations being readied for neuclear reaction could be fixed thereon and because such materials would not undergo degradation or transformation when subjected to high density neutron flux. Organic ion exchange materials should not be used since they do not meet the second criterion, but certainly other inorganic exchangers may be substituted in lieu of those specifically named in the present specification.

For explanatory purposes I wish to next consider a schematic reaction sequence using .for purposes of ex-' This is the basic exchange reaction by which exchangeable sodium ions are replaced by M ions. Such reaction is known to follow the law of mass action and thus Accordingly, the replacement can be made substantially quantitative either by the use of excessive M+ or the successive removal of the Na+ in repeated treatments.

. 3 The second reaction of interest involves the fixation'of the M+: a a

' Aging M(Na-clay) NaM(M-elay) This reaction likewise is an equilibrium process. If necessary the final sample can be made extremely high in fixed Mt simply by repeated aging and replacement of exchangeable Na+ with additional M .In the case of montmorillonite clays I have foundthat more than 90% of the originally exchangeable cations can be fixed by heating the clay samples containing the desired cation at 700 C. for approximately 2 to 3 days.

' The third reaction is the replacement of the exchangeable Na+ and M+ by NH or H At this stage the M ions are either non-exchangeable or only exchangeable with great difficulty. Such cations are thus quite effectively held within the Al--OSi lattice structure. Next one should. consider the situation when the M+ nuclei are bombarded with neutrons and undergo an (my) process. The M nuceli would then receive, because of momentum conservation, energy which may be as much as several hundred electron volts and in any event considerably in excess of what is needed to overcome the lattice forces in the Al--OSi structure. Thus we have the fourth reactioni In other words, those M nuclei which have been neutron activated may be projected out of the lattice structure and can therefore be readily separated from the bulk One aspect of my invention therefore is directed to a' modified Szilard-Chalmers process for the preparation of radioisoto-pes.

. My inventi'on rnay be best understood by. consideration of the'following examples thereof: 7

EXAMPLE I 1 Preparation of cobalt In this series of experiments the aluminum silicate used was. bentonite clay. Sodium-potassium-bentonite, U.S.P. grade wasfurther purified and hydrated by re-. peated washing with water and recovering the clay by centrifugation. Initially such purified clay was then treated with 300 ml. of N HCl, collected on a Biichner funnel and then repetedly leached with additional amounts of 2N HCl until no potassium and sodium ions were detectable by the flame test. a The combined I-ICI s01 tions containing the exchangeable potassium and sodium ions were analyzed by flame photometry to determine the cation exchange capacity of suchclay to be 79.7 millequiv alence per 100 grams of clay.

Research Foundation boiling water reactor or in the CP.5 reactor of the Argonne National Laboratory. In all cases referenced cobalt standards were irradiated with the clay samples to provide information concerning any possible fiuxations in the integrated neutron fluxes.

EXAMPLE II Preparation 0 .bal izmz from barium:

In this process the treatment steps are very similar to those which are set outin the example presented above. The same type of clay was used and was purified in the same manner as in the cobalt experiments. In this case the clay samples were treated with a dilute solution of BaCl collected on a Biichner funnel and repeatedly leached with additional amounts of BaCl solution until the filtrate contained no sodium or potassium ions detectable by flame tests. The amount of barium ions introduced based on that of sodium and potassium ions exchanged and as determined by flame photometry, was found to be 68.3 millequivalents per 100 grams of clay.

Finally the barium bentonite obtained was heated for 48 hours at 700 C. in order to accelerate the barium ion fixation onto the clay. The extent of the Ba ion fixation in these clay samples, based upon the amount of Ba ions, subsequently eluted with HCl amounted to 76.9% of the Ba ions originally introduced into the sample...

The fixed barium-bent'o'nite clays were thenirradiated for-time periods ranging from 20 to 25 minutes in the ARF reactor where the neutron flux is 6 10 neutrons cinf secr In this case saco, was used as the reference standard.

Following irradiation the barium-bentonite samples were eluted twice with dilute solutions of either HCl or CH CGONH of predetermined concentrations. Following such treatments the supernatant liquids containing the released Ba ion were separated byycentrifugation and decantation, concentrated by evaporigation and then transferred into a glass counting vessel (containing approxi-" mately 0.2 grarn of NH NO which was added to aid subsequent handling) and finally evaporatedto dryness. Thedried samples containingthe barium isotope were measured by means of an RC1 256 channel ditterential pulse heightanalyzer using a 3 x 3 inch Nal (Tlactivated) crystal.

Enrichment factors were determined for both the cobalt and barium samples.

Asnoted above-following irradiation the nuclei produced were extracted. This was accomplished 'eithen by ion exchange procedures (i.e., treating the irradiated clay samples vwith dilute solutionsof HCl or NH Cl) or Following this determination of the enrichrnent factor,

was carried out 'by neutron activation analysis for the presence of stable .cobaltf59 or barium- 138 nuclei in I the extracted sample using the formula Another aliquot of the purified and hydrated sodiumipotassium-bentonite. was contacted with dilute aqueous solution of cobaltous chloride, collected on a Biich'ner' funnel and repeatedly leached withCoCl solution until the filtrate was free of sodium and potassium ions as detected by the flame test. This Co-clay was then driedand calcined at approximately 700720 C. for periods ranging from 48 to 72 hours to effect the cationrfixation.

Subsequently the clay was treated to remove as much as possible of the exchangeable cobalt contained therein.

, represent respectively the counting rate of a sample be- 1 This step of the process was accomplished either by'leach- 1 ing with aqueous HCl solution or electrolytic extraction.

f Spec. activity of the extract Spec. activity if no enrichment 0 net (re-exp.) V V C' C'; nvt (original) forthe C o-60 C nut (re-exp.) samples, (if F mttoriginal) Enrichment f actor= for the Bar-138 samples. (In these formulae, C and C 'fore and after re-exposure for neutron activation analysis,

whereas nvt (re-exp.) and nvt (original) representrespectively the integrated fluxes used in the activation analysis.

and in the original hot-atom experiment. The diflerence between the formula for Co-60 'and that for Ber-139' is due to the short half life of the latter'nu'clei).

The results of our experiments showed'that the en richment factors achieved are approximately 20 or higher" Enrichment Factor Enrichment Factor D COBALT-6O CHEM (mt) (re-exp.) (nut) (original) COBALT-60 ELEC- (m1!) (re-exp.) (mt) (original) Counting Data Re-exposure c.p.m.), (01) Original (0 Counting Data Re-exposure c.p.m.). (01) Original (0 l. 10X10 1. 46X10 1. 1].)(10 1. 57x10 7. 46 l0 11 7x10 considerable extent on the prior treatment of the clay samples as well as on the method of extraction.

The following tables present some of the results of the hereinabove experiments.

TABLE l.COUNTING DATA AND ENRICHMENT FACTORS SELECTE ICAL ELUTION EXPERIMENTS Sample Identification 03 in the case of-Co-GO, and approximately 3 in the case of Ba-139. The enrichment factors achieved are not sensitively affected by the intensity of the neutron flux oversome three orders of magnitude, but are dependent to a M-Feb TROCHEMICAL ELUTION EXPERIMENTS Sample Identification TABLE 2.-OOUNTING DATA AND ENRICHMENT FACTORS SELECTED TABLE 3.EFFECT OF ELUENT CONCENTRATION L. 561 855 88 42 t @416 604 409 661 626 n .1 .6 w fl w G 6 6 6 666 6 6 5 45 7. 666 e 665 655 765 665 N mm 1 m0 C t 3 mm S mF .1 S .1 F I m E m E 1 t] I2 1?! w 11 ill. 1 a] 1] n n n m R 0 O 7 1 9 m n n P mfl a 3 2 1 2 mm N N N N E 060 2 C N. m n w N N a H 0 1 1 2 2 A Y MW 0 0 0 .0 0 W 1 .lmol. rlwl. W 1 1 1 1 269 12 309 746 751 I M 333 33 33 333 33 3 6 T m mmm mmm mmm mmm mmm H2 310 310 320 420 620 A m 5 XXX XXX XXX XXX XXX ed I .0 521 794 746 900 361 mfl D m. 560 470 857 004 935 M A :IW 882 32 932 215 42 R a R m a M 338 333 333 333 333 333 D 33 .333 333 333 331 m mww wmw www www mmm mmm N g WNW mmm mmm mmm mww J XXX wh NN New.. We E m m New Wk New New.. New W m. Wawwn 28% $21 088 121 419 W m e 891 901 595 191 9.44 5. 6 0 nu I .11 1 5 2 1 5 LL L0 3 6 2L J 852 1 B n 2 1 1 h r m o t m E a D B 2. WWW WWW m mum mmv o 3mm WWW D 123 123 123 123 123 m 111 111 111 111 111 111 E m XXX New e.. eel NW New t u NBS 84.8 H86 585 57- 1 11 M o i n 4 l e r 1 05 562 C O 531 842 721 63 1 1 1 L N E E [111. (I41 flllk 1 123 123 123 1 123 M 1 2 5 9 m .5 1 I ne 8% T Smw W m Wm mm m w D \I J EN MM T F L 1 L rl l. C .n0 E u n u n u (n F .m u u u u u n mmr n n J n 0 n n n E w u 1 la m Jr m n n n n Dc WM 4 m u n mm u n J E e n n n a n .0 Sn re L I e c B d f .E I 1.. 2 A H 5 w mm A p 1 2 3 Am 5 J J J J J i. T m e 4 V V V V V S V V V V V 1 mt (re-exp )lnvflorieinal) =5.(). 5 Percent of radionuclide formed.

TABLE 5.EFFECT or INTEGRATED NEUTRON FLUX Exposure Counting Data (c.p.ml) Time Efiluent (re'exll) Enrichment Sample Identification (days) Number not (original) 7 Factor Original Re-exposure 1 It is to be noted that enrichment factors actually appear to become higher with increasing integrated flux. This could be due to the diminishing relative importance of the residual exchangeable cobalt-59 ions remaining in the system as the amount of -60 increase.

TABLE 6.COUNTING DATA AND ENRICHMENT FACTO RSBARIUM EXPERIMENTS Zero Time Counting Rates (e.p.m.) Ba Standards (mg) g Enrich- Sample Identification Eluted Ba Eluted Ba With With ment factor Numbers 1 Ba-138 Standard Ber-139 Standard original eluted ADE and Irradiated after reused in resample 1321-139 Ba-l39 with clay irradiation irradiation (A) (0) (E) F MIG-l7 3. 05 10 6. 50 l0 1. 07Xl0 5. Zi0 10 I 6. 5.08 3.10 6. 39x10 4 10 3. 08Xl0 1. 95x10 1.95 0.975 V 1. 90 1. 91 l0 3. 05 10 8. 00 l0 3. 10X10 0. 835 0. 766 2. 64 2. 72 l0 7. 70 10 9. 74x10 1. OBXlO 0. 766 1. 04 2. 88 1. 68 l0 1. 76x10 6. i7 (10 7. x10 1. 46 0. 766 2.08

1 Two numbers are used for each set of experiments. One is for the original sample, the other for the reirradiated elution product.

It will be understood that various modifications and variations may be effected without departing from the spirit or scope of the novel concepts of my invention.

' I claim as my invention: 7

1..Ihe method of making radioisotopes which comprises the steps of: introducing cations to be made radioactive to an inorganic cation exchange material which is r resistant to neutrons and other ionizing radiation and which is further characterized by the ability to fix such cations within its lattice structure; fixing said cations in said cation exchange material; removing not-fixed canons;

irradiating said ion exchange material-fixed cation composite with neutrons to produce radioactive product nuclei of said cations and concurrently defixing such radioactive product nuclei; and separating such radioactivenuclei from the ionexchange mass.

2. The method of carrying out a nuclear reactionwhich comprises the steps of: introducing cations to 'be made radioactive to an inorganic cation exchange material which is resistant to neutrons and other ionizing. radiation and which is furthercharacterized by the ability to fix such cations within its lattice structure; fixing said cations in 1 said cation exchange materiah removing not-fixed cations; irradiating saidion exchange material-fixed cation composite with nuclear radiation to produce radioactive product nuclei of said cations and concurrently defixing such cations and. concurrentlydefining'such cations and sepa- 7 rating said cations from the exchanger mass.

4. The method of making cobalt which comprises the.

steps of: introducing ions of cobalt to an inorganic cation exchange material which is resistant to neutrons and other ionizing radiation and which is further char-* acterized by the ability to fix such ions within its lattice structure; heating said cobalt containing ion exchange material at approximately 700 C. for at least 24 hours 40 to fix said ions in said cation exchange materiah'removing not-fixed barium; irradiating said'ion exchange'material-cobalt composite with neutrons to produce cobalt and concurrently defixing such cobalt, and separating such cobalt from the ion exchange mass.

5. The method as defined by claim 4 wherein said inorganic cation exchange material is an aluminum silicate clay. 1 V

6. The method of making barium. which comprises the steps of introducing ions of barium to an inorganic 5O cation exchange material which is resistant to neutrons and other ionizing radiation and whichis further characterized by the ability to fix such ions within its lattice structure; heating barium containing ion exchangernaterial at approximately 700 C. for' at least 24 hoursto fixsaid ions insaid cation exchange material; removing not-fixed cobalt ions; irradiating said ion exchange mate such cobalt from the ion exchange mass; 7 (30 7. The method-as defined by claim 6 wherein said inorganic cation exchange'rnaterial-is an aluminum silicate clay 7-.

8. Themethod of making cobalt which comprises'the steps of introducing ions of cobalt? to an inorganic cation exchange material which is resistant to neutrons and other ionizing radiation and which is further characterized by moving not-fixed cobalt; irradiating said ion'exchange materiail-cobalt composite with neutrons to produce cobalt and concurrently defix such cobalt fi'an d separating such cobalt from the ion exchange mass.

7 the steps of; introducing ions of barium to an inrial-cobalt composite.with neutrons to produce cobalt and concurrently defixing such cobalt, and separating the ability to fix such ions' within its lattice structure; fixing said cobalt ions in said cation exchange material; re-

9. The method of making barium which comprises organic cation exchange material which is resistant to neutrons and other ionizing radiation and which is further characterized by the ability to fix such ions within its lattice structure; fixing said barium on said cation exchange material; removing not-fixed barium; irradiating said ion exchange material-barium composite with neutrons to produce barium and concurrently defix such barium and separating such barium from the ion exchange mass.

References Cited by the Examiner UNITED STATES PATENTS 1,592,543 7/26 Stewart 252455 1,617,476 2/27 Christopher 252-455 2,780,517 2/57 Fontana 176--16 2,887,357 5/59 Seaborg et a1. 17616 CARL D. QUARFORTH, Primary Examiner. L. DEWAYNE RUTLEDGE, Examiner.

' {Paren -No; 3,167,479 f Attesting Officer vvu ru rm) STATE-SJPATENT OFFICE cERTiFIc T-E 10F CORRECTION PauI Y. F e ng It is hei'ebj certified .tha'blex 'ro r gppe ars in the aBovenumbered patent requiring correction and that the said Letters .Patent should read as corrected-below. P

Column 8-',,' line 41, fbr."barium" read 56", for "cobalt" read barium line "57 for- "colghltw" read barium 3 ,'-;"s'ame,- line 57 and 'l inles 58 and 59', for "cobalt each occurrence, read --barium I cobalt line Signed and sealed t hiQZ S'th day of February 1969,

Attst: I Edward M. Fletcher, Jr. EDWARD- J. Cbmmissioner f Patents -January 2.6, 1965 um'rm) STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,167,479 January 26, 1965 Paul Y. Feng It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column .8, line 41, for "barium" read cobalt line 56, for "cobalt" read barium line 57 for "comaltw" read barium same line 57 and lines 58 and S9, for "cobalt each occurrence, read barium Signed and sealed this 25th day of February 1969,

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. THE METHOD OF MAKING RADIOISOTOPES WHICH COMPRISES THE STEPS OF: INTRODUCING CATIONS TO BE MADE RADIOACTIVE TO AN INORGANIC CATION EXCHANGE MATERIAL WHICH IS RESISTANT TO NEUTRONS AND OTHER IONIZING RADIATION AND WHICH IS FURTHER CHARACTERIZED BY THE ABILITY TO FIX SUCH CATIONS WITHIN ITS LATTICE STRUCTURE; FIXING SAID CATIONS IN SAID CATION EXCHANGE MATERIAL; REMOVING NOT-FIXED CATIONS; IRRADIATING SAID ION EXCHANGE MATERIAL-FIXED CATION COMPOSITE WITH NEUTRONS TO PRODUCE RADIOACTIVE PRODUCT NUCLEI OF SAID CATIONS AND CONCURRENTLY DEFIXING SUCH RADIOACTIVE PRODUCT NUCLEI; AND SEPARATING SUCH RADIOACTIVE NUCLEI FROM THE ION EXCHANGE MASS. 